Field of the Invention
The present disclosure relates to an organic light emitting diode display, and particularly, to an organic light emitting diode display which can minimize a malfunction due to an open failure caused in a fabricating process of the organic light emitting diode display using thin film transistors as control elements, and fabricating and inspecting method of the organic light emitting diode display.
Description of the Related Art
A liquid crystal display, a field emission display, a plasma display panel, an organic light emitting diode display (OLED display), and the like are used as flat panel displays for substituting for cathode ray tubes.
Among these displays, organic light emitting diodes provided in the OLED display have characteristics of high luminance and low operating voltage, and are self-luminescent. Hence, the OLED display has a high contrast ratio and can be implemented as an ultra-thin display. Also, the OLED display has a response time of a few microseconds (μs) to easily realize moving pictures. Also the OLED display has no limitation of a viewing angle, and is stable even at low temperature.
FIG. 1 is an equivalent circuit diagram of a pixel of an OLED display according to the related art.
Referring to FIG. 1, the pixel PX of the OLED display has a structure having three thin film transistors SWT, DRT and SST and one capacitor C1, and includes an organic light emitting diode EL; a driving thin film transistor DRT for supplying current to the organic light emitting diode EL; a scan thin film transistor SWT for receiving a data voltage Vdata, the scan thin film transistor SWT being connected to the driving thin film transistor DRT to the data voltage Vdata to a gate electrode of the driving thin film transistor DRT according to a scan signal Vscan; a sensing thin film transistor SST connected between a sensing controller and the driving thin film transistor DRT to sink the current supplied from the driving thin film transistor DRT according to a sensing signal Vref; and a capacitor C1 connected between the gate electrode and a source electrode of the driving thin film transistor DRT.
In order to implement realize high resolution images that require high quality of full-HD or more in the OLED display, each pixel should be configured to have a high aperture ratio structure. The high-resolution display has a high probability that a failure such as corrosion, non-patterning or step difference failure may occur in a fabrication process of the high-resolution display, as compared with the existing high-resolution displays. Accordingly, a defect detection method and an efficient repair method are required.
Particularly, in the OLED display having the pixel structure described above, there frequently occurs a failure that a line for connecting between the source electrode of the driving thin film transistor DRT and an anode electrode of the organic light emitting diode EL is opened. The lines are formed in different metal layers to be contacted with each other, and the upper metal layer is over-etched in an etching process due to a step difference of the lower metal layer, thereby resulting in the failure.
FIG. 2 is a sectional view illustrating an example in which an open failure occurs in the OLED display according to a related art.
Referring to FIG. 2, in the OLED display, a gate metal layer 13, a gate insulating layer 15, a first source and drain metal layer 22, a passivation layer 25, a second source and drain metal layer 27, an interlayer insulating layer 31 and an anode metal layer 43 are sequentially formed on a substrate 10.
Such a structure is referred to a face seal structure. In the structure, the second source and drain metal layer 27 acts as an auxiliary gate electrode of the driving thin film transistor (DRT of FIG. 1). That is, the driving thin film transistor has a dual gate structure in which the gate electrode of the driving thin film transistor is configured with two metal layers, i.e., the gate metal layer 13 and the second source and drain metal layer 27.
As shown in this figure, the passivation layer 25 performs a function of insulating the first source and drain metal layer 22 beneath the second source and drain metal layer 27. The passivation layer 25 has one side opened so that the anode metal layer 43 is electrically connected to the first source and drain metal layer 22 through the second source and drain metal layer 27.
In an etching process of the second source and drain metal layer 27, the second source and drain metal layer 27 is over-etched due to a step difference caused by the lower passivation layer 25, and therefore, an open failure frequently occurs in the second source and drain metal layer 27. Accordingly, an electrical signal is not normally applied to the anode metal layer 43.
This becomes a factor that causes an unexpected malfunction of the OLED display, thereby deteriorating the driving reliability of the display.